Prior to the present invention bi-polar lead-acid and other electric charge storage batteries have been made with positive and negative electrode plates interleaved in the cells of the battery. A first end cell of the battery may have positive electrode plates with projecting lugs that are joined to a connector strap of a positive battery terminal of a lead based alloy (hereafter lead). Another end cell of the battery may have internal negative electrode plates with projecting lugs that are joined to the connector strap of an external negative terminal usually identical to the positive terminal. Similarly, the positive plates of intermediate cells (i.e., between the end cells) are likewise joined with a positive plate strap which in turn is connected to a negative strap in the next adjacent cell via an intercell connector. This lug-strap connection is generally made by arc welding, torch flaming the straps, until the strap material amalgamates or fuses with the material of the lugs. This fusing is generally done with the use of comb-like containers/tooling installed over, and interdigitating with, the lugs prior to their fusion with the strap to prevent strap material from flowing between and short circuiting the interleaved positive and negative plates resulting in the scraping and recycling of the electrode assembly. Alternatively, the strap may be cast directly in place using the so-called "cast-on-strap" process wherein the lugs are positioned in a mold on molten lead cast thereabout. Generally, the assembly of the straps and plates is made outside of the battery case and is and then inserted in the battery case. An electrolyte is then added and the case is subsequently sealed to prevent electrolyte leakage.
The present invention contemplates a unique method of joining plate lugs to a precast plate strap. The invention shall hereafter be described in conjunction with joining the plates in the end cell of a battery to a battery terminal, but is not restricted thereto. Rather the process is equally applicable to joining the plates of intermediate cells to plate straps destined for coupling to other plate straps in contiguous cells of a multicell battery. In a preferred embodiment of the terminal-electrode plate welding of the present invention the positive and negative electrode plates are interleaved in their respective cells with the plates interlayered with glass mat separators. The plates and separators are within a battery case of a heat sensitive material such as polypropylene. The negative electrode plates are identical and have lugs extending through a slotted pocket in one wall of the battery case. Similar lugs of the positive electrode plates extend through a slotted pocket in another wall of the case. Subsequently, small beads of glass, or other suitable particulate insulating material (e.g., cut glass fibers, polypropylene particle, sand, etc.), are fed and vibrated, or brushed into one of the slots through which the lugs of one set of the electrode plates extend. These beads form a bed of predetermined thickness which tightly nest around and between the lugs to provide a barrier or seal so that during welding the molten lead-based metals of the strap and upper portions of the lugs will not flow into areas of the interleaved positive and negative plates. This effectively eliminates short circuit between adjacent plates. Before welding, the extending lugs and terminal strap are appropriately fluxed (e.g., with a powdered Azelaic acid) so that the strap burn or weld zone is accordingly fluxed to assure a clean surface for optimization amalgamation of the lugs and the strap. By special alignment and insulation construction associated with the wall of the casing, the terminal is accurately positioned on with the plate strap portions overlying the lugs. Thereafter an induction coil is lowered into contact with the strap and into a burn position. The coil is energized at a predetermined percent of induction generator power (e.g., 85-90% depending on the size of power unit) for a predetermined time, six seconds for example, so that the strap and upper portions of the lugs are fused together. After the burn, the coil is removed and the strap and lug amalgamation area is allowed to completely solidify to complete the connection of the first terminal to the plates of one polarity (e.g., negative).
The battery is then turned so the unburned lugs are upright or otherwise accessible and the process is repeated to affix a terminal to the second row of lug of the other electrode plates.
These and other features, objects and advantages of the invention will become more obvious from the following detailed description and drawings in which: